If you're thinking about dividing your tank, the best thing to do (in my opinion) is to empty the tank and put your fish(s) in temporary homes. Take the empty tank to a Lowes or Home Depot and look for the plexiglass. Try it in the tank. If it doesn't fit, a store employee can help cut it for you. It's much easier to have your tank with you than to explain "Two males/females can't be in the same tank.. but I measured it...etc." You'd get home, it'd be an inch off, then you'd have to drive back to Lowes!
(Note:You can cut the glass to be just a bit taller so it's snug, but it won't look symmetrical. Water still flows too because it isn't butt-up against the sides. I reccomend moving the heater as close to the divider as possible.)

As for the filter (if your fish are getting sucked up, that is) You bring your filter intake tube with you, go to the pipe section, find a clear, bendy pipe (like the ones on gravel vacuums) get an employee to fit/cut it down to the right size, then you're good to go.
(If you're worried about it making the flow weak, it doesn't. You may have to adjust some decor though.
The other good news is that the flow is good, but not strong enough to even suck up a piece of gravel! (if you have smaller fish like ADF'S.)
(You can also opt for one with a smaller hole, too.)